Terence Rattigan's stage play, The Winslow Boy, was based on the famous Archer-Shee case, which became something of a cause célèbre due to extensive newspaper coverage. Twelve-year-old naval cadet Ronnie Winslow is accused of stealing a five-shilling postal order and expelled from Naval College. Father Arthur Winslow believes his son's innocence and fights in court with the help of famous KC Sir Robert Morton. The family undergoes much sacrifice, but Ronnie's innocence is eventually proven.

Anthony Asquith's adaptation continued the long association with Terence Rattigan and Anatole de Grunwald, who co-adapted the screenplay. Contemporary critical reaction was mixed, with some disappointed in Asquith's lack of adventure in reworking the material for the cinema, although The Sunday Times considered it "one of the best British films of the year, with a background... beautifully precise as to period, class and place". Asquith certainly captures the texture of middle-class Edwardian era Wimbledon and the atmosphere of the House of Commons (where his father had served as Prime Minister some four decades earlier).

Despite the film's title, the character of the boy remains largely unexplored. His mother reminds Arthur that he's 'only a child', and although Morton consistently argues for the boy's right to a fair hearing, the film itself is guilty of denying him a voice, ignoring Ronnie in favour of the adult characters, particularly Arthur, Catherine and Morton. These characters play out the main themes of the film, and it is through examination of their motives that we question whether a fight for justice is fuelled by pride, and ask what sacrifices are worth making for a point of principle.

A seemingly whimsical gesture in which Morton passes a letter urging 'Let right be done' to the First Lord of the Admiralty, who returns it with a curt 'Impossible', encapsulates the film's moral universe. Arthur, Catherine and Morton all suffer for their principles, but the scene questions the importance of their fight. This is particularly poignant considering their world is about to be changed beyond recognition by the looming war in Europe. Nevertheless, the film concludes by championing the importance of individual rights, a cause Morton believes in so strongly that he is willing to sacrifice his career for it.